This invention generally relates to the construction and manufacture of bags and more specifically to a bag structure that facilitates opening and reclosing of a bag and the apparatus for manufacturing such a bag.
Bags are used for storing a wide variety of contents and are composed diverse materials. Although this invention can be utilized and applied to many different bags, it is particularly suited for bags that are used for packaging snack foods and the like and that are composed of thin cellophane or organic polymer base material that has limited tear resistance.
Hundreds of millions of these bags are manufactured each year. They are manufactured in a combined form-and-fill apparatus. More specifically, in such apparatus sheet material is drawn past a guide which directs the material into a tubular form surrounding a mandrel. As the material is drawn along the mandrel, an overlapping seam is formed in the material sealed by a heat or pressure sealing process. The material is thus formed into a tube as it passes over the mandrel. The material then passes heat sealing jaws that are disposed to form a transverse heat seal across the tube thereby to simultaneously "form" an upper seal in one bag and a bottom seal on an adjacent bag. When this occurs, the contents can "fill" the bag through a passage in the mandrel. The resulting bag then contains a longitudinal seal along the material seam and seals at the ends that define an hermetically sealed pouch for the contents. The sealing jaws normally also contain a mechanism for severing the completely sealed bag for subsequent shipment. This "form-and-fill" manufacturing process is widely accepted because it is reasonably simple, requires a minimal number of operations, and is reliable.
However, bags formed by this process are not without their problems as purchasers of snack or like contents of such bags are well aware. The bags can be difficult to open and do not facilitate reclosure if the contents are only partially consumed. Typically a purchaser will attempt to open the bag either by tearing through the seal or by trying to separate the seal. When an attempt is made to tear through the seal, the tear detection and length are random. The nature of the material is such that the tear could travel in any direction and depending on the force utilized to start the tear could travel for various distances. If the purchaser grabs the oppositely spaced walls of the pouch and then tries to pull the walls apart to separate the seal, a random opening also can occur. Specifically the force required to separate that seal varies widely and is not predictable. In either case, the opening procedure is not controlled or predictable. As a result, the bag oftentimes tears and is thus destroyed. Moreover, whether the bag tears or not, the operation often causes the contents to spill.
Generally these bags contain perishable contents or contents that become stale if exposed to air. If the contents of such bags are only partially consumed, it is not easy to reclose the bags thereby to preserve the freshness of the remaining contents. The open end of the bag, assuming it remains intact during the opening procedure or opening operation, can be rolled up; however, at rest the bag tends to resume its original shape and the rolled portion straightens thereby opening the bag and exposing the contents to air. Thus it is difficult to reclose the bag without some separate element.
A great deal of research and development has been expended in order to provide a bag which is easy to open and which can be simply reclosed. A number of solutions have been proposed.
Some bags have been designed in an attempt to solve both the opening and reclosing problems. Generally these bags include some structure for assisting or directing the tear and some separate, removable element that can be used to reclose the bag if the contents are only partially consumed. For example, U.S. Pat. No. 3,184,149 discloses a resealable bag. This bag includes a sheet of flexible material having a structure for cutting through the side of the bag to expose the contents for consumption or use. If the contents are only partially utilized, a protective layer formed in a top seal portion is removed to expose a coextensive area of adhesive material. When the top of the bag is folded down against itself, the adhesive material adheres to the bottom seal to close the bag. U.S. Pat. No. 3,224,640 discloses a bag having at least three walls. The contents are stored in a pouch between the first and second walls. The bag includes a tear line partially through the seal. As the top is torn off the bag, the contents are exposed. A slit is formed in the third wall to receive the top of the bag after it is folded over. U.S. Pat. No. 3,618,850 discloses a bag in which a pleated foil strip is affixed to the bag just below one of the end seals. The bag is opened by tearing through the seal. The foil serves as a tear stop and guides the tear transversely across the bag. If the contents are only partially consumed, the top of the bag can be folded about a transverse axis that passes through the foil. The pleats in the foil tend to retain the folded shape of the foil and thereby keep the bag closed.
Another group of bag designs are characterized by a tear strip that can also be used to reclose the bag. U.S. Pat. Nos. 3,311,288 and 3,426,959 disclose such bags. More specifically, a tear strip is affixed transversely across the bag into one wall in the area of the pouch. When the tear strip is pulled, it rips the bag under the tear strip and exposes the contents. Once the tear strip has been removed, it can be saved to reclose the bag by being wrapped around the bag. U.S. Pat. No. 3,480,198 discloses a bag in which a tear line is formed across the bag in one or both of the walls of the pouch inwardly of the heat seal; that is, in the walls that are separated to form the pouch. The tear line is formed by apertures through both side walls that are fused around their circumferences so that the seal is not broken until the bag is torn along the tear line. The resulting top can then be removed to form a tie for the remaining contents of the bag. However, this action does not open the bag completely.
U.S. Pat. No. 3,613,874 discloses a bag in which a pressure sensitive adhesive is applied as in U.S. Pat. No. 3,184,149. A tear strip is also provided to tear away a portion of the bag; it has a fairly high tensile strength and is bonded to the film forming the bag rather strongly in such a way that the strip will not break or pull away from the film but will overcome the film's tear strength when it is pulled thereby tearing the bag. U.S. Pat. No. 3,619,395 also discloses a plastic bag with a tear strip in the form of a ribbon which is pulled to tear the bag. This bag contains a releasable fastening means on the inner, opposed wall surfaces which enables the bag to be resealed.
The individual problem of facilitating the opening of these bags has also been the subject of research and development. Another general approach can be characterized as providing tabs above the seal or outside the seal for facilitating the opening. These approaches are exemplified in U.S. Pat. Nos. 3,397,835 and 3,419,137, and British Pat. No. 620,354. In U.S. Pat. No. 3,397,835, for example, a corner portion, or inset, is heat sealed and includes a tear line. When the bag is opened, the portion outside the tear line is removed; then the opposite walls of the bag in the inset, which are not sealed together, can be grasped individually to facilitate opening of the bag. Another approach has been to add structure to a bag that will limit or direct the tear tearing during opening. Folding the bag material to produce folded portions around the bag are shown in U.S. Pat. No. 2,053,116. The use of transverse beads to limit the tear is shown in U.S. Pat. Nos. 3,323,707 and 4,139,643. Other examples are shown in U.S. Pat. Nos. 3,412,918 and 3,179,327. The use of special chemical treatments by placing a coating between the heat sealable surfaces before bonding to facilitate opening is shown in U.S. Pat. No. 3,511,436.
A concept for facilitating the closure of paper bags is disclosed in U.S. Pat. No. 2,023,855. Tabs are formed in one wall of the bag. This wall extends beyond the other wall and slits are formed in the other wall. On closure the extended wall is folded over the other and the tabs are then inserted through the slits; other corresponding or analogous closures are also shown.
These various prior bag configurations have not gained wide, if any, commercial acceptance. They are all characterized by being more expensive to manufacture than a conventional bag. This added expense has not justified the acceptance of these configurations by the manufacturers of the contents that fill the bag. There are several reasons for this added expense. Many of the bags require the addition of discrete elements such as tear strips, or releasing agents. Others require special manufacturing apparatus or processes to provide multiple seals, to insert separate elements, to fold or configure the bags. Still others require an increase in the amount of bag material that is utilized to form the bag. Because of these and other reasons the industry, particularly the snack food industry, continues to package contents in a tubular bag with a longitudinal seal and two plain end seals and without any means for facilitating the opening or the reclosing of the bag.